The
Airpods contain an infrared sensor, accelerometer, microphone and possibly other
sensors, this could provide a brand new wearable hardware platform for health and medical
sensing. For example core body temperature, maybe heart rate detection. The
accelerometer could be used for head position sensing e.g. head nods "yes"
or shaking "no". This could be very useful for some applications.
Head accelerometers have also been used to measure concussion in sport, e.g. football.
The Airpods will use bidirectional digital communication, so could not use the old analogue 3.5mm socket. At least with Bluetooth, if you drop the Airpods, you can find them if location within a few metres, the iPhone will show nearby Bluetooth devices.

Image below from Apple of inside an Airpod.

We
can see the infrared sensor, the dark cylinder in image, possibly a
thermopile which allows none contact temperature sensing, e.g. of the
human body in seconds. Here an example of a thermopile from Texas Instruments. It is the small reflective semiconductor, U5, size 1.8mm x 1.8mm.

Below shows a thermal image of an ear, revealing the core body temperature, a healthy 38C. The colder blue is the outer ear. This image taken with an array of 80 x 60 thermal sensors.

Passif designed the custom wireless semiconductor. More here
about Passif technology. An interesting patent from Passif in this
Fast Company article describes an energy harvesting system from radio
waves.

Apple
own
the earliest patents on a mobile phone with infra red human proximity
detection, and accelerometer control. I invented and built a handheld
computer design in 1997, the first phone
that used these sensors. The patent was purchased by Apple in 2011
as
here, patent for Apple.